The invention relates to a system for generation of oxygen by low-temperature air separation by low-temperature air separation having                a high-pressure column and a low-pressure column,        a main condenser which is constructed as a condenser-evaporator, wherein the liquefaction space of the main condenser is flow-connected to the top of the high-pressure column and the evaporation space of the main condenser is flow-connected to the low-pressure column,        an oxygen product line that is connected to the low-pressure column,        an auxiliary column,        means for introducing a gaseous fraction, the oxygen content of which is equal to that of air or higher, into the sump region of the auxiliary column having        a reflux liquid line for introducing a liquid stream from the high-pressure column, the main condenser, or the low-pressure column as reflux to the top of the auxiliary column, wherein the liquid stream has a nitrogen content that is at least equal to that of air.        
The fundamentals of low-temperature air separation in general and also the structure of two-column systems especially, are described in the monograph “Tieftemperaturtechnik” [Low-temperature technology] by Hausen/Linde (2nd edition, 1985) and in an essay by Latimer in Chemical Engineering Progress (Vol. 63, No. 2, 1967, page 35). The heat exchange relationship between high-pressure column and low-pressure column of a double column is generally implemented by a main condenser in which overhead gas of the high-pressure column is liquefied against evaporating sump liquid of the low-pressure column.